The present invention relates to a method for the preparation of an oximesilane compound. More particularly, the invention relates to an efficient method for the preparation of an oximesilane compound without the risk of forming an oxime hydrochloride having explosiveness and unavoidably formed in the prior art methods.
An oximesilane compound, such as methyl tris(methyl ethyl ketoxime) silane of the formula MeSi(--O--N.dbd.CMeEt).sub.3 and vinyl tris(methyl ethyl ketoxime) silane of the formula ViSi(--O--N.dbd.CMeEt).sub.3, in which Me is a methyl group, Et is an ethyl group and Vi is a vinyl group, is a useful organosilicon compound to serve, for example, as a crosslinking agent in certain types of room temperature-curable organopolysiloxane rubber compositions. These oximesilane compounds are prepared in the prior art by the method disclosed, for example, in Japanese Patent Publication 39-29837, according to which a chlorosilane compound such as methyl trichlorosilane MeSiCl.sub.3 is subjected to a dehydrochlorination reaction with an at least stoichiometrically equivalent amount of an oxime compound such as methyl ethyl ketoxime of the formula MeEtC.dbd.N--OH in the presence of an excess amount of an organic base such as pyridine as an acceptor of the hydrogen chloride produced by the dehydrochlorination reaction. A problem in this method is that, while it is necessary to isolate the desired oximesilane compound from the hydrochloride of the organic base, e.g., pyridine hydrochloride, by distillation, hydrochlorides of an organic base are sometimes explosive to cause serious explosion during the distillation procedure.
It is also proposed in Japanese Patent Publication 1-21834 that the dehydrochlorination of a chlorosilane compound for the preparation of an oximesilane compound is performed in the presence of an oxime compound in an amount twice as large as the stoichiometrically equivalent amount and the excess of the oxime compound serves as an acceptor of the hydrogen chloride so that addition of a separate organic base compound is not required. This method is also not free from the danger of explosion during processing of the reaction mixture since hydrochlorides of an oxime compound are generally explosive. In addition, oxime compounds are generally expensive so that the hydrochloride thereof cannot be discarded as such necessitating facilities for the recovery and recycling of the oxime compound from the hydrochloride thereof.
It is further proposed in Japanese Patent Kokai 63-227592 that the dehydrochlorination of a chlorosilane compound and an oxime compound is performed while ammonia gas is blown into the reaction mixture to serve as an acceptor of the hydrogen chloride so that an oximesilane compound can be prepared in a continuous process. A problem in this method is that the reaction must be performed under control of the temperature of the reaction mixture by using a non-inflammable halogenated hydrocarbon solvent such as perchloro fluorinated alkanes, trichlorotrifluoroethanes and the like, most of which are industrially banned due to the problem in the environmental pollution.